1. Field of the Invention
The present invention relates to an illumination optical system unit for an endoscope that irradiates a portion to be observed inside a subject with illumination light to observe inside the subject, and a method of manufacturing the illumination optical system unit for an endoscope.
2. Description of the Related Art
In the past, diagnosis using an endoscope has been widely used in a medical field. An endoscope includes an observation window which is formed at a tip of an insertion section to be inserted into a subject and through which image light of the subject is taken, and an illumination window through which illumination light is emitted to the subject. The endoscope is connected to a light source device through a cord or a connector. The light source device includes a light source for supplying illumination light for the illumination inside the subject to the endoscope. The illumination light supplied from the light source is guided to the tip of an insertion section through an optical fiber that is inserted into the endoscope.
A white light source, such as a xenon lamp or a halogen lamp, could have been used as the light source of the light source device. A ratio of a space, which is occupied by the white light source and peripheral components of the white light source, to an inner space is high in a light source device using the white light source, which makes it difficult to reduce the size of the light source device. For this reason, a light source device using a laser light source instead of the white light source has been used in recent years. JP2007-20937A and JP2011-72424A disclose an endoscope that irradiates inside a body cavity with white illumination light by guiding laser light, which is supplied from the light source device using the laser light source, to a tip of the insertion section through an optical fiber and exciting a fluorescent body, which is disposed at a tip of the optical fiber, by the laser light to allow the fluorescent body to emit light.
Further, the endoscope needs to emit illumination light having higher intensity. For this reason, a reflective film having high reflectance is provided around the fluorescent body to efficiently use the light or the like, which is excited and emitted, as illumination light. It is known that a metal film made of silver, aluminum, or the like is suitable as the reflective film having high reflectance.
However, in diagnosis using an endoscope, moisture level is high in the insertion section of the endoscope inserted into the body cavity and grease containing molybdenum disulfide is applied to movable components and the like, which are used to bend the insertion section, as a lubricant. Further, the endoscope is subjected to washing and disinfection process, in which the endoscope is immersed in disinfectant containing peracetic acid and the like, after diagnosis. Since water or grease and chemicals, such disinfectant, easily enter the insertion section of the endoscope as described above, the degradation of the fluorescent body or the reflective film easily affected by water or chemicals may easily occur.
Further, a projection unit (an illumination optical system unit for an endoscope) disclosed in JP2011-72424A includes an outer cylindrical member as a sleeve member that covers the outer periphery of the fluorescent body, sapphire glass as a protective cover that covers the tip side of the fluorescent body, and a ferrule as a holding member that holds an optical fiber and is disposed at the base end side of the fluorescent body. The base end side of the outer cylindrical member is sealed while the optical fiber extends, and the tip side of the outer cylindrical member is sealed while adhering to the sapphire glass.